1. Field of the Invention
The present invention relates to a linear motor driver, and more particularly to a linear motor driver for driving a permanent magnet movable type linear motor by partly exciting a movable element employed therein.
2. Description of the Conventional Art
Generally speaking, a linear motor employs a stator containing coil block and a movable element containing permanent magnets. The coil block and the permanent magnets are installed parallel to each other in a horizontal direction, respectively, so that the coil block faces the permanent magnets.
The supply of an electric current into the coil block of the stator generates a thrust force between the coil block and the permanent magnets under Fleming""s left-hand rule. The generated thrust force permits direct linear motion of the movable element along the longitudinal direction of the stator.
A conventional linear motor made it possible such a direct linear movement is disclosed in U.S. Pat. No. 4,595,870, which will be described below. FIGS. 1 and 2 used in the referenced patent application are also here shown, in which FIG. 1 is a perspective view of a linear motor according to the prior art, and FIG. 2 is a control system for the linear motor shown in FIG. 1.
FIG. 1 shows a configuration of the conventional typical linear motor 10. The linear motor shown in FIG. 1 includes a U-shaped channel 12 and a movable element 18. The U-shaped channel 12 mounted on a mounting surface (not shown) encloses a wound stator 16. On an upper surface of wound stator 16, the movable element 18 is disposed to be moved in a direction indicated by a double-headed arrow 22.
Movable element 18 includes a plurality of permanent magnets (not shown) facing upper surface 20 of wound stator 16 for producing a magnetic field for interaction with the magnetic field produced by the coil block (not shown) of wound stator.
Referring to FIG. 2, a control system is employed which controls generation of magnetic fields between the stator 16 containing coil block and the movable element 18 containing a plurality of permanent magnets, and further controls a thrust force created due to interaction between the magnetic fields produced.
Control system 28 receives commands from a host (not shown). Upon receipt of commands, control system 28 receives through information channel 30 positional information representing positional relationship between the permanent magnets 32 of movable element 18 and respective coils 24a, 24b, 24c of the stator 16, and in response thereto, the control system 28 selectively controls the switches 26a, 26b, 26c to control an application of power supply into each of coils 24a, 24b, 24c. 
On the other hand, the above-described control system, which is used to selectively control said switches 26a, 26b, 26c, receives information through the information channel 30 when the movable element 18 leaves the coil 24a, and in response thereto, opens the switch 26a connected the coil 24a to block the supply of the power supply. Namely, the control system 28 serves to partly excite the respective coils 24a, 24b, 24c based upon the movement of the movable element 18.
The above-described prior art uses a magnetic sensor and a Hall-effect device (not shown) in order to partly excite the respective coils 24a, 24b, 24c provided to the stator 16. In the case of the use of such a magnetic sensor and the Hall-effect device, the magnetic fields from the permanent magnets in the movable element causes an erroneous operation of the Hall-effect device, which results in malfunction of the linear motor.
Therefore, an object of the present invention is to provide a driver for a linear motor which senses position of movable element to partly excite coils provided to a stator, with the influence of magnetic fields from permanent magnets directly associated with thrust force of the linear motor being minimized.
Further, another object of the present invention is to reduce power consumption by partly exciting respective coils of the stator and to minimize heat generation by selectively exciting respective coils.
To accomplish the above-mentioned objects, this invention provides a driver for a linear motor, the driver comprising: a stator having coil block and disposed on an inner bottom surface of a U-shaped frame; a movable element having a plurality of permanent magnets at an armature frame; a shield member provided on one side surface of the movable element, and having a magnet sensing unit formed on one side surface thereof for blocking magnet fields generated from the plurality of permanent magnets; and a controller board disposed on an inner wall of the U-shaped frame, and for sensing magnet fields generated from the magnet sensing unit to selectively supply an electric current into the coil block.
Thus, an erroneous recognition of the position of the movable element can be prevented which may occur due to the magnet fields generated from the permanent magnets used for creating a thrust force of the motor. Therefore, an optimum driving condition for the linear motor can be accomplished. Further, by partly exciting the coils to drive the movable element, the power consumption by the coils can be reduced, and heat generated when the current flows into the coils can be minimized.